In a previous post, you learned that evolution is a theory, and a theory is something that all the scientific evidence supports. In another post, you learned about the theory of evolution. But, how did the theory of evolution come about? What was the evolution of evolutionary thought? Well, in order for the theory of evolution to be developed, some ideas needed to change.
In the first post in this series, we looked at ideas about the relationship between humans and other forms of life. In the second post, we looked at ideas about the age of the Earth. Next, in the third post, we looked at ideas about fossils and what they implied about life. Then in the fourth post, we looked at ideas about adaptation to the environment. Now, we will explore Charles Darwin’s ideas, and how he integrated all these ideas we discussed.
Charles Darwin attended Cambridge and studied geology and botany. After he graduated, he was invited to take part in a 5-year long scientific expedition that would go around the world. So Darwin went, and he was able to collect data from all around the world.
During his time on the Galapagos Islands off the coast of Ecuador, Darwin studied finches–a type of bird. He noticed that there was a wide variety of finches–the finches were different on each island, but they all were similar to the finches on the mainland. And on each island, the finches were different in different habitats. For example, the finches on the coast of the islands were different than finches living in the middle of the islands.
One difference between finches was beak shape and size. Heavy thick beaks were used for eating seeds and leaves, while long thin beaks were used for catching flying insects, and long thick beaks were used to eat insects inside of trees.
Each environment had a finch with a different kind of beak, and so Darwin realized that these beak variations were adaptations to the environment. Those finches with certain variations would do better in certain environments, and have a better chance of living and having offspring. For example, if there is a finch with a long beak and a finch with a short beak in a place where finches have to eat insects inside trees, then the one with the long beak is more likely to live and reproduce.
So, Darwin knew that there was lots of variation in each species. And he took Malthus’ idea of competition for resources. So, he proposed that some variations made an animal better adapted to their environment, and so they were able to outcompete those with other variations, and they passed those adaptive variations onto their offspring.
Darwin was familiar with animal breeding, and knew that breeders select certain animals who have certain traits to breed so that the offspring will have those same traits. And the breeders don’t select other animals who have unwanted traits. As a result, some traits are enhanced while others are eliminated. Darwin felt a similar thing was happening in nature, but it was nature, not humans, doing the selection of traits. So he called the process “natural selection.”
Darwin thought that over a long period of time, a new species could form from the process. If groups within a species get separated, like into different islands, then different traits will be adapted to each different environment. Over time, one species can end up as multiple species. Darwin felt that was what happened with the Galapagos finches—they had all descended from a common mainland ancestor, and the one species had changed over time into multiple species in response to different environments and types of food available.
So, Darwin had a theory of evolution based on natural selection, and he had a lot of evidence for it. But he wasn’t ready to go public yet, and so he gathered more data for about 20 more years. He finally only published his ideas when Alfred Russel Wallace came up with the same idea because Darwin was afraid that Wallace would get all the credit.
Did you ever hear the saying, “standing on the shoulders of giants?” This means making discoveries that were built upon previous discoveries. This is exactly what Darwin did. He knew that humans were related to animals (not separate), based on the work of Ray and Linnaeus, and so he applied his evolutionary theories about animals to humans. He knew that the Earth had been around for a long time from Hutton and Lyell, long enough for a process like evolution to happen. He knew that one species could change into new ones, based on the work of his grandfather, Erasmus Darwin. And, he developed ideas about organisms and their adaptation to the environment from the ideas of Lamarck and Malthus. All these ideas of other people contributed to Darwin’s theory of natural selection.
In summary, Charles Darwin’s trip around the world gave him the data he needed to come up with his theory of evolution by natural selection. Studying finches showed him that certain traits are advantageous in certain environments, and these traits allowed an organism to outcompete others for resources. Then, over time, new species can result from increasing differences in groups adapting to different environments.
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Thanks for reading!